Hitherto, ethyleneimine polymers have been widely utilized in the fields of paper processing agents, adhesives, pressure sensitive adhesives, paints, inks, textile treatment agents, coagulative separating agents, cosmetics, toiletries, dispersing agents, and the like. However, it is difficult to conduct the polymerization of ethyleneimine while controlling the polymerization temperature, the molecular weight, the branch structure, and the like since ethyleneimine is highly reactive, and thus various methods for polymerizing ethyleneimine have been proposed.
A method for producing an aqueous solution of an ethyleneimine polymer having a concentration of from 25 to 50% and a high molecular weight is disclosed in JP 43-8828 B, JP 2001-213959 A, JP 2001-288265 A (US 2001/039318 A1). Specifically, a method for producing an aqueous solution of an ethyleneimine polymer is proposed in which ethyleneimine is polymerized in the presence of water and a catalyst such as a polyhalogenated compound represented by 1,2-dichloroethane.
The aqueous solution of an ethyleneimine polymer thus obtained is the aqueous solution of an ethyleneimine polymer which has the highest molecular weight in the current industrial level. Specifically, the number average molecular weight (hereinafter, abbreviated as Mn) of the ethyleneimine polymer measured by gel permeation chromatography (hereinafter, also referred to as “GPC”) in terms of pullulan of the molecular weight standard substance is 10,000 or more.
However, the ethyleneimine polymer obtained by the above method does not exhibit sufficient adhesive properties compared to the used amount in the case of being used in an application such as an adhesive, and thus it is desired to develop an ethyleneimine polymer which can secure sufficient adhesive properties when used in a smaller amount.